Present day automobiles are being increasingly loaded with accessories including the engine fan; alternator for the battery; air conditioning; and pumps for servo-operations such as automatic shifts, power windows, power steering, power brakes, and the like. Such accessories have been designed to operate satisfactorily at engine idling speeds and continue satisfactory operation at top engine speeds, but the result of such an arrangement is to severely limit the performance of the engine. This is true because even though at their optimum speeds, the total power consumption of the accessories is only a few horsepower; at high speeds the accessories are less efficient and power consumption may be ten to twenty percent of the engine output. One way of handling this problem is to provide a variable speed drive arrangement to provide a fairly constant accessory speed as the engine reaches the necessary speed for operation of the vehicle. However, such a variable speed drive system is relatively complicated in construction and operation. The present invention obviates the above problem in providing a simplified and efficient accessory drive system.
Present U.S. automobile manufacturers are in general using such low numerical rear axle ratios that an accessory drive has limited value. With the advent of lighter, smaller cars, the car manufacturers will change to smaller and lighter engines and will run them at higher rpm levels; resulting in the use of high numerical rear axle ratios. For example, a first small car presently manufactured will use an 85 or 97 C.I.D. engine with a 4.11 to 1 rear axle ratio and weigh aproximately 2000 pounds. This compares to a second small car in production having an 140 C.I.D. engine with a 2.92 to 1 rear axle ratio (using a four speed transmission) and a weight of approximately 2600 pounds. The first car requires the 4.11 to 1 rear axle ratio to obtain reasonable performance. The second car's engine will turn 2366 rpm at 55 mph while the first car's engine will turn at 3330 rpm. Thus, higher rpms will be a trend in future smaller cars.
The present invention relates to a simple two-speed accessory drive which employs the two rotating shafts on an internal combustion engine; namely, the crankshaft and the camshaft. The camshaft runs at 50% of crankshaft speed, and through design of the drive system, this ratio of camshaft to crankshaft rpm can be utilized to arrive at a better choice of accessory rpm ranges. The accessory is driven directly by the crankshaft from idle to a predetermined speed level of the crankshaft where the efficiency of the accessory drive will tend to decrease at increasingly higher rpms. Then a suitable clutching arrangement allows the camshaft, operating at 50% of crankshaft speed, to take over the drive of the accessories and the rpm of the accessory drive will again increase but at a lower speed than that of the crankshaft.
Another object of the present invention is the provision of a two-speed accessory drive for an internal combustion engine wherein a centrifugal clutch arrangement is utilized to provide for release of the crankshaft drive and a one-way clutch provides for engagement of the camshaft drive. The accessory drive pulley is mounted on a stub shaft in alignment with and connected to the crankshaft through the centrifugal clutch mechanism; the stub shaft being suitably mounted in a bearing on the engine. A drive sprocket connected to the camshaft through a drive chain is mounted on and operatively connected to the stub shaft through a suitable one-way clutch, such as a sprag clutch.
The present invention also provides an accessory drive for an internal combustion engine wherein a slipping clutch is utilized between the crankshaft and the stub shaft carrying the pulley for the accessory drive. The use of the slipping clutch will provide a time interval of substantally constant rpm during which the crankshaft is released from the stub shaft and before the camshaft takes over the accessory drive through a one-way clutch. This arrangement will omit a sharp drop in the speed of the accessory drive and provide a smooth transition.
Further objects are to provide a construction of maximum simplicity, efficiency, economy and ease of assembly and operation, and such further objects, advantages and capabilities as will later more fully appear and are inherently possessed thereby.